Purpose

The rev limiter on a car is there to prevent over-reving, which will destroy the engine.  Most gasoline cars designed for street use have a limiter somewhere around 6000-7000 RPM.  Some sports cars have it set slightly higher to allow the engine to make more power in the high RPMs.

Simply removing the rev limiter, without making any other modifications to a car, will do next to nothing.  In some cases, being able to rev the engine higher will yield slightly better performance, often at the cost of more engine wear.

You should only worry about raising the rev limiter once you've done substantial work to the engine.  My personal advice would be to have at least the full exhaust upgraded (including the exhaust manifold and downpipe), a sport camshaft and some way to get more fuel to the engine.

The stock exhaust really restricts everything, so don't even think about removing the rev limiter if you're still running the stock exhaust.  The stock camshaft is designed to make power in the stock rev range, so there really isn't any reason to raise the rev limiter if you still have the stock camshaft installed.  About the only reason I see to raise it when you're still running with the stock camshaft would be so you don't accidentally hit it (when, driving competitively on the street, or in another similar situation).  Once you install a sport camshaft you will want to raise the rev limiter so you can use the power the camshaft makes above 6000 RPM.  You should also give the engine some more fuel and richen up the mixture a bit if running a sport camshaft, and if running in the high RPMs.  (Read this about getting more fuel to the engine.)

If you're worried about running your car to some really high RPMs, don't.  Unless you build an all-out race car, you will not be reving past 7000-8000 RPM.  Any car that makes good power above 7000 makes little power below 4000-5000 RPM, and is not by any means a street car.  Phillip's 16v race Fox was built to be able to rev up to about 10,000 RPM, but he doesn't need to go past 8000 on the track.

If you check Techtonics Tuning's Camshaft Specs page, you will see that even their race camshafts do not make power above 7500 RPM.  So even if you go crazy with the camshaft, you won't be revving your engine to ridiculous heights.
[Note: I have no affiliation with Techtonics, other than using some of their parts in my cars.]

1987-1990
On CIS and CIS-E Foxes (1987-1990) it is possible (and very easy) to remove the rev limiter.  The fuel pump relay gets a signal to stop the fuel above 6000 RPM.  To bypass this, all you have to do is use a horn relay in place of the fuel pump relay in your fusebox.  This makes the fuel pump run anything time the key is in the "on" position (compared to only when the engine is running with a fuel pump relay).  If you do replace the fuel pump relay with a horn relay, and should you be in an accident, be SURE to turn the key to "off", otherwise the fuel pump will keep on running, causing a very dangerous situation.


1991-1993

It is impossible to raise the rev limiter beyond 6000 RPM on the Digifant Foxes.  The rev limiter is built into the the ECU itself, and there is nothing we can do.  The question of an aftermarket chip will come up - I have contacted every maker of chips for VWs, and no one makes one, and no one will make one for the Fox.  The reason is because the Fox does not have a knock sensor;  without a knock sensor a chip cannot safely advance the ignition timing (one of the key ways a chip makes more power).

The only options on Digifant Foxes would be to:

• Transfer the knock-sensing ignition and computer from another Digifant VW (Golf/Jetta), and then get a chip for that ECU.
• Go with an aftermarket ignition and possibly fuel injection setup.
Both of these are quite time consuming and expensive.  Unless you have some serious money to put into your car, I would recommend sticking with the 6000 RPM redline.  I am still stuck with it.
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